Splits post-processed offline drmemtrace files into chunks of a fixed instruction count. These chunks are combined inside one zipfile per thread, maintaining the current file-per-thread invariant.
The minizip library, a contributed part of the zlib sources, is added as a submodule and used to write and read the zipfile (via new zipfile_ostream_t and zipfile_file_reader_t classes, respectively). If the submodule is not present, we fall back to a gzipped single file (if we have a system zlib).
Issue: #5538